Processes for synthesizing optically active alcohols by asymmetric hydrogenation of carbonyl compounds have hitherto been reported. For example, Y. Ohgo proposed asymmetric hydrogenation using bis(dimethylglyoxymato)cobalt (II)-quinine as a catalyst as described in Chem. Lett., 709-712 (1974). However, this process attains such poor results as 2.5 to 73%ee in optical yield of the resulting alcohol and 10 to 20 in a substrate/catalyst molar ratio.
It has been also been proposed to use a rhodium-optically active phosphine as a catalyst as disclosed, e.g., in I. Ojima et al., J.C.S. Chem. Commu., 428-430 (1977) and T. Hayashi et al., Tetrahedron Lett., No. 48, 4351-4354 (1976).
According to the process using the cobalt-optically active amine, not only the alcohol produced has low optical purity but the catalytic activity is not sufficient.
Further, in the process of using the rhodium-optically active phosphine, metallic rhodium to be used in the catalyst is expensive due to limitations in place and quantity of production. When used as a catalyst component, it forms a large proportion in cost of the catalyst, ultimately leading to an increased cost of the final commercial products.